Congenital Dislocation of the Knee (Pediatric)

Synonyms
Congenital genu recurvatum, CKD

INTRODUCTION

Definition

A hyperextension deformity of the knee with anterior tibia displacement that is present at birth.

Epidemiology

  • Rare disorder that is commonly sporadic but occasionally occurs within families.
    • CKD incidence has been reported at 1 in 100,000 live births.
  • Bilateral congenital dislocation of the knee is almost always associated with other syndromes, such as Ehlers-Danlos syndrome, Larson syndrome, or Beal syndrome.

Etiology

  • Unknown etiology. It may be due to decreased intra-uterine space or fetal malposition, congenital absence of the cruciate ligaments, and fibrosis and contracture of the quadriceps.
  • Conditions producing muscle imbalance or laxity that are associated with congenital dislocation of the knee are myelodysplasia, arthrogryposis and Larsen syndrome.

Patoanatomy

  • The spectrum of disease include rigid dislocation to mild positional contractures.
  • Structural components include:
    • Quadriceps contracture.
    • Tight collateral ligaments.
    • Anterior subluxation of hamstring tendons.
    • Absent suprapatellar pouch.

Classification

Tarek CDK Classification: Graded by passive range of flexion and radiologic appearance. This classification can guide treatment.

Tarek CDK Classification
GradeRange of passive flexionRadiology
Grade 1> 90°Simple recurvatum
Grade 230-90°Subluxation/dislocation
Grade 3< 30°Dislocation

CLINICAL FEATURES

Symptoms

Hyperextended knee is seen at birth.

Signs

Inspection:
  • The knee is hyperextended, and the foot is easily placed against the baby’s face. 
  • There might be a dimple or transverse skin crease at the anterior knee (due to a shortened, sometimes fibrotic quadriceps).
  • There may be rotatory or valgus deformity of the tibia.
  • The hamstrings may displace anteriorly and act as extensors.
Movement/ROM: Minimal or no flexion of the knee is possible.
  • General laxity from cruciate pathology or displaced collateral ligaments may be seen.
  • It is important to examine the hip because ipsilateral hip dislocation is very common.

Associated Conditions

Congenital dislocation of the knee is associated with:
  • Developmental hip dysplasia (50 % will have concomitant DDH affecting one or both hips).
  • Clubfoot (up to 47 %).
  • Metatarsus adductus.
  • Breech presentation (up to 30%).

DIAGNOSIS

Ultrasound (USG)

Prenatal ultrasound may identify CKD.

X-ray

Radiographs are used as a confirmatory study. 
  • Grade 1 and 2: Confirm contact between the femoral and tibial epiphysis.
  • Grade 3: Epiphyses are not in contact and the tibia is anterior to the femur.

TREATMENT

Overview

It is important to prioritize the treatment of the knee dislocation over treatment of ipsilateral hip dysplasia or clubfoot. Knee flexion is required for the Pavlik harness and clubfoot casts.  

Nonoperative Treatment

Indication: Initial treatment because most cases can be treated nonoperatively.
  • Tarek grade 1.
  • Initial treatment for Tarek grade 2 (up to 1 month of age).
Method: Stretching, followed by reduction with manual manipulation and serial casting (long leg cast) on weekly basis.
  • Attempt flexion only after the tibia is reduced on the end of the femur. This must be confirmed with lateral radiograph or ultrasound, because it is possible to get distal femoral physeal separation or plastic deformity of the tibia.
  • Treat the knee first when there is a concomitant DDH. This is because the Pavlik harness cannot get on and stay on the hip if the knee is dislocated.
  • A botulinum toxin injection may be used in severe quadriceps contracture to assist with progressive stretching and knee flexion.
  • A study shows that clubfoot casting may be carried out simultaneously with casting for CKD.

Operative Treatment

Surgical soft tissue release:
  • Indication:
    • If nonsurgical treatment fails to reduce the tibia on the end of the femur, i.e. failure to gain 30° of flexion after 3 months of casting.
    • Tarek grade 2 (identified after 1 month of age).
    • Tarek grade 3.
    • Recurrent cases.
  • Goal of surgery: To obtain 90° of flexion.
  • Method: A release that includes quadriceps lengthening. Best results are seen when surgery is performed in children younger than 6 months. Techniques include:
    • Percutaneous quadriceps recession (PQR).
    • Quadriceps tendon lengthening (V-Y quadricepsplasty or Z lengthening).
    • Anterior joint capsule release.
    • Posterior transposition of hamstring tendons.
    • Mobilization of collateral ligaments.
    • Recent studies advocate for femoral shortening osteotomy to produce relative lengthening of the quadriceps mechanism.
  • Postoperative care: Cast in 45-60° flexion for 3-4 weeks

COMPLICATIONS AND PROGNOSIS

Complications

Epiphyseal deformity: May be caused by closed reduction attempts without first applying traction to clear the tibia distally from the femur.
Residual hyperextension: May persist after casting.
Laxity/valgus deformity: May be found in some post-operatively.
Quadriceps insufficiency: May be associated with open reduction and quadriceps lengthening. 

Prognosis

Generally excellent prognosis if reduction is achieved nonsurgically.
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References